Rechargeable nickel-metal hydride (NiMH) batteries are used in a variety of industrial and commercial applications such as fork lifts, golf carts, uninterruptible power supplies, pure electric vehicles and hybrid electric vehicles. Vehicular applications include applications related to propulsion as well as applications related to starting, lighting and ignition.
One aspect of battery operation that is particularly important for electric vehicle and hybrid vehicle applications is that of thermal management. In both electric and hybrid vehicle applications individual electrochemical cells are bundled together in close proximity. Many cells are both electrically and thermally coupled together. Therefore, the nickel-metal hydride batteries used in these applications may generate significant heat during operation. Sources of heat are primarily threefold. First, ambient heat due to the operation of the vehicle in hot climates and second, resistive or I2R heating on charge and discharge, where I represents the current flowing into or out of the battery and R is the resistance of the battery. Third, a tremendous amount of heat is generated during overcharge due to gas recombination.
A battery generates Joule's heat and reaction heat due to electrode reaction at charging and discharging operations. A module battery including a series of cells having such a large capacity or a pack battery including a series of the module batteries is configured of several tens to several hundreds of the cells arranged contiguously to each other. The cells, with an increased electric capacity and sealed configuration, increase in the amount of heat accumulation, with the result that heat dissipation out of the battery is retarded and the generated heat is accumulated within the battery. Consequently, the internal temperature of such a battery rises by a degree more than that of a smaller battery. U.S. Pat. No. 5,879,831 hereinafter “831 Patent”) discloses battery module having a plurality of individual batteries secured by bundling/compression means welded at the corners to restrict the batteries from moving or dislodging when subjected to mechanical vibrations of transport or use. U.S. Pat. No. 5,663,008 (hereinafter “008 Patent”) discloses a module battery having a plurality of cells secured between two ends plates and band-like binding members for coupling the endplates. The primary purpose of the design disclosed is to prevent deformation of the synthetic resin battery casing.
While issues regarding heat dissipation are generally common to all electrical battery systems, they are particularly important to nickel-metal hydride battery systems. This is because NiMH has a high specific energy and the charge and discharge currents are also high. Second, because NiMH has an exceptional energy density (i.e. the energy is stored very compactly) heat dissipation is more difficult than, for example, lead-acid batteries. This is because the surface-area to volume ratio is much smaller than lead-acid, which means that while the heat being generated is much greater for NiMH batteries than for lead acid, the heat dissipation surface is reduced.
In addition, while the heat generated during charging and discharging NiMH batteries is normally not a problem in small consumer batteries however, larger batteries (particularly when more than one is used in series or in parallel) generate sufficient heat on charging and discharging to affect the ultimate performance of the battery.
Thermal management issues for nickel-metal hydride batteries are addressed in U.S. Pat. Nos. 6,255,015, 6,864,013 and U.S. patent application Ser. No. 10/848,277 are all of which are hereby incorporated herein by reference.
An example of a monoblock battery is provided in U.S. Pat. No. 5,356,735 to Meadows et al, which is incorporated by reference herein. Another example is provided in U.S. Pat. No. 6,255,015 to Corrigan et al, which is hereby incorporated by reference herein.
Currently there exists a need in the art for a modular battery system that provides stability for individual modules and thermal management of the system to reduce, among other things, overheating of the system, deformation of the casings and shock to the system. Further, there exists a need in the art for a modular battery system that utilizes a battery management system to monitor the performance and status information of each battery module in the modular battery system and which has flexibility for a wide variety of applications.